The present invention relates to a server-client network system, and more particularly to the network technique which is arranged to-curtail loads burdened on the network and a server and provide a comfortable working environment to each client.
Before describing the invention, the following four known arts will be described.
(1) Domain Name System (DNS)
The internet employs a system that uses a domain name represented by hierarchically setting each logical group called a domain and delimiting the logical group with a period.
The correspondence between a domain name and an IP address, (which corresponds to a network address in the internet, for example, the address being represented by figures delimited with some periods) is managed by a DNS server. The DNS server operates to swap information with another DNS server if necessary. The swapping operation results in making it possible to correspond all the domain names to the IP addresses included in the internet.
A client makes access to a destination server for providing the target service the client would like to reach through the use of the internet. For this purpose, in actual, the client uses the IP address that is a physical address in place of the host name. It means that the client has to obtain the IP address of the server for providing the target service the client would like to reach.
If, therefore, the client does not know the IP address of the server for providing the target service, the client indicates the domain name of the target server to the DNS server pre-registered as its own server for inquiring the IP address of the target server. In response to the inquiry, the DNS server searches the corresponding IP address to the domain name of the target service server and notifies the client of the IP address.
In addition, if the DNS server of inquiry cannot obtain the IP address of the service server, the DNS server inquires the upper DNS server of it.
(2) Proxy Server
Between a network inside of an organization that needs high security and the internet located outside of the network, a firewall for access control is normally built. The proxy server is a proxy gateway developed in effect when the communications inside or outside of the organization are prohibited by the firewall.
For example, inside of a local area network (referred to as an LAN), a user cannot directly communicate with a wide area network (referred to as a WAN). To overcome the inconvenience, a segment area called xe2x80x9cBarrier Segmentxe2x80x9d is provided between the LAN and the WAN, so that the client user temporarily has to do remote log-in to the server operating on the barrier segment and then makes access to the server on the WAN side.
This method, however, needs to prepare many user accounts (right of use given in the user registration) in the server operating on the barrier segment. This disadvantageously leads to increasing the security holes.
Under these circumstances, a proxy server has been developed which allows the server or the client of the network inside of the organization to access a resource or data of Gopher, WWW or the like without having to prepare any user account for the server operating on the barrier segment.
The proxy server is operated on the firewall. The proxy server keeps special ports open so that it can receive messages from plural clients. Then, the proxy server operates to transfer the received messages to the server for providing the target service the client would like to reach. It thus serves to be proxy for the client.
The proxy server receives a message from the client without user authentication. The proxy server uses the IP address that corresponds to the physical address of the client for the communications with the client, so that the log-in of the client to the proxy server is unnecessary if not specified.
The proxy server has a function of relaying a client""s access to the resource or the data of the Gopher or the WWW, for example. The client just communicates with only the proxy server without direct communications with the server on the WAN side.
This proxy server eliminates the necessity of directly exchanging the message between the LAN and the WAN, thereby making it impossible for the WAN side to unjustly attack the LAN side.
(3) Proxy Cache Server
When developing the foregoing proxy server, a proxy server provided with a cache function has been developed as its byproduct.
The proxy server has been developed for the purpose of relaying the client""s access to the resource or the data. Hence, highly plausibly, two or more clients on the LAN side may refer to the data at a time.
If two or more requests for referring to the data takes place, the proxy server refers to the data of the server on the WAN side and gives back the data to the clients on the LAN side who have issued the referring requests.
As mentioned above, the proxy server may operate to temporarily cache the resource or the data referenced once by itself in a storage medium such as a disk and give back the data temporarily cached in the disk to the clients on the LAN side who have issued the referring requests without having to access the server on the WAN side if two or more requests for referring to the resource or the data given by the clients take place at a time. The proxy server provided with this type of function is referred to as a proxy cache server.
The proxy cache server helps to curtail the traffic on the WAN. It is more advantageous to the user, because the communications on the WAN is lower in speed and higher in cost than those on the LAN.
Moreover, the reduction of the access times given from the client on the LAN to the server on the WAN makes great contribution to lessening the load burdened on the server. Further, the user on the LAN can reuse the resource or the data cached in the proxy cache server that is a local server, so that the user may enjoy a comfortable response to the access.
In addition, the proxy cache server may make sure of a time stamp of the resource or the data cached in a storage medium such as a disk so that it may access the server on the WAN again about the resource or the data having the previous time stamp than a given period. This operation allows the proxy cache server to obtain the resource or the data of the latest version.
(4) Client-Store System
As an inexpensive internet access device of the next generation, an inexpensive terminal is designed wherein only the internet function and protocol to be supported as minimum level are mounted.
This type of terminal has to support as minimum functions many internet communications protocols such as Web and FTP (File Transfer Protocol) and a networking standard service of a network sharing system, a UDP (User Datagram Protocol), a TCP (Transmission Control Protocol), a DHCP (Dynamic Host Configuration Protocol), a BOOTP (Bootstrap Protocol), and the like.
Unlike personal computers, it is preconditioned that this type of terminal requires the server to concentratively manage all the applications and the promotion. However, this type of terminal does not include a harddisk. Hence, each time it is started, the application program has to be downloaded from the server. This results in disadvantageously increasing the load burdened on the server and the network.
In place of this type of terminal, a system is also provided for reducing distribution of the application program from the server to a minimum through the use of the harddisk of the existing personal computer.
When the resource is transferred from the server, this type of system operates to record the resource in the harddisk and reuse the resource recorded in the harddisk if necessary.
This system does not need to constantly read the resource from the server. Further, in using the resource or periodically, the system is operated to check change of the resource on the server. It thus has an advantage that the resource of the latest version may be constantly started on the client side. On the other hand, however, this type of system would be more disadvantageous in portability and cost than the ordinary portable terminal.
The conventional DNS is a system for obtaining an IP address for a physical address of a server from a domain name received from the client in a one-to-one manner when the client makes access to the server. However, it has the following disadvantages.
In a case that two or more servers for providing the same service are located distributively on the network, it is difficult for the client itself to determine the most approximate server to the client user, because the client has to manage the name of each server, determine the most approximate server, and request the service of the server. This operation is quite annoying.
Further, in a case that there are two or more networks each of which has two or more servers for providing the same service distributively located thereon, the user of the client has to access the proper server by considering the conditions of the load burdened on each network and each server.
Moreover, in a case that two or more servers for providing the same service are located distributively on the network, for keeping the comfortable response in working, the user of the client has to access the server consciously of a physical or a logical distance between the server and the client.
Herein, two or more servers for providing the same servers distributively located on the network concretely may include the conventional proxy server and the conventional proxy cache server.
However, the conventional proxy server (hereafter, the term xe2x80x9cproxy serversxe2x80x9d includes the xe2x80x9cproxy cache serverxe2x80x9d.) has no means for authenticating the user of each client. The use of this proxy server, therefore, makes it impossible to provide the service for each user.
Further, the terminal having no storage device such as a harddisk cannot employ the foregoing conventional client-store system.
Moreover, if the client makes use of the application program that needs to frequently communicate with the server, the client cannot satisfactorily meet the processing.
For example, in a case that the application program (for example, the access to the database or the client-server type Kana-Kanji transformation) includes many processes of enabling the client to transmit a message to the server and obtaining the response from the server, the accesses from the client are concentrated on the server, so that the loads burdened on the server and the network are increased. In particular, in the case of using a low-speed network such as the WAN, the response on the client side is made remarkably inferior.
In order to overcome the foregoing shortcomings, a system is considered for distributing many proxy servers on the network, bringing each client in correspondence to a local proxy server closer thereto, and prompting the corresponding proxy server to access the target server. However, this system has a new disadvantage that the management of each proxy server is more costly.
Further, in a case that many proxy servers are distributively located on the network, the proxy server and the client are required to set the network address for corresponding both to each other. Once it is set, the dynamic change of the setting is quite difficult. Further, the user account of the client is managed only by the corresponding proxy server, the user cannot do any work on a client of another place.
It is a main object of the present invention to provide a comfortable working environment to a client in which only by specifying a logical node name of a server for providing a target service the client would like to reach, the most approximate proxy server to the client can be automatically selected in consideration of the loads burdened on the network and the server and the location of the client.
It is another object of the present invention to provide a comfortable working environment to the client in which the traffic on the network and the load burdened on the server are curtailed.
In order to achieve the foregoing object, unlike the conventional DNS server that manages the stationary correspondence between the domain name and the network address, the dynamic DNS server according to the present invention is arranged to manage the location information and the load conditions of the proxy servers distributed located on a network, constantly select the proxy server having the most approximate access environment to a client based on the location information of the client and the managed content when notifying the client of an address of the server corresponding to the domain name inquired by the client, and notify the client of the address of the selected proxy server, for the purpose of solving the problem about the address of the proxy server. Moreover, if just one proxy server is located on a network, the present invention can offer the proper effect. Concretely, when the dynamic DNS server according to the present invention determines that the proxy server can offer the more comfortable access environment to the client than the server for the domain name inquired by the client, the dynamic DNS server operates to notify the client of the network address of the proxy server in place of the network address of the server for the domain name.
In the foregoing DNS server, merely by specifying a logical node name of the server from which the client would obtain the service, the client can make access to the most approximate proxy server that is selected in consideration of the loads burdened on the network and the server and the location of the client. Hence, the dynamic DNS of the invention can provide the user of the client with the comfortable working environment without lowering a response characteristic.
It is preferable that the location information is a combination of logical location information for the network address and physical location information for the information representing a connecting location on the network. The latter information may be selected as an area code of a place where the proxy server is located or a latitude and a longitude of the proxy server.
In order to obtain the load conditions of the proxy server, the proxy server may be arranged to give back the load condition of itself in response to an inquiry sent from a proxy server selecting unit or autonomically notify the proxy server of the load condition at periodic terms.
In order to achieve the foregoing another object, the dynamic DNS server according to the invention is arranged to distributively locate plural proxy servers on a network so that the proxy server may communicate a resource or data with the server through another path rather than a path through which the server provides its service, for the purpose of curtailing the traffic and the load of the server.
In the foregoing dynamic DNS server, for example, the proxy server may be arranged to obtain a resource on the server through another path rather than the path through which the server provides its service. In this arrangement, if communications between the client and the server frequently take place, the proxy server can provide the client with the comfortable working environment.
Further, for example, the proxy server may be arranged to communicate the proper user data to the user of the client and the information thereabout with the server through another path rather than the path through which the server provides its service if necessary. In this arrangement, the proxy server can implement the service for each user without managing the user account.
According to the present invention, the proxy server selecting unit (corresponding to the foregoing dynamic DNS server) is provided to manage the location information and the load condition of the proxy servers distributively located on the network, when notifying a client of the address of the server for the domain name inquired by the client, select the most approximate proxy server to the client based on the location information of the client and the managed content, and notify the client of the address of the selected proxy server.
Merely by specifying the server from which the client would obtain the service, therefore, the client can constantly make access to the most approximate proxy server when accessing the server. The server selecting unit can provide the user of the client with the comfortable working environment without lowering a response characteristic.
According to the present invention, the proxy server is arranged to communicate the resource or data with the server through another path rather than the path through which the server provides its service.
The proxy server, therefore, provides a capability of downloading the resource or data located in the server and caching it on the timing when the request from the client is received and providing the client with the cached resource or data, for the purpose of curtailing the traffic and the load of the server.
In particular, in a case that the server manages the resource or data for each user, the proxy server enables to download the resource or data required by the user of the client for accessing the proxy server itself from the server, cache it, and then provide the client with the cached resource or data.
Further, if a client""s access to the server frequently takes place, the proxy server is arranged to download the resource or data existing in the server, cache it, and provide the client with the cached resource or data. In this arrangement, the proxy server makes it possible to curtail the traffic and the load of the server and provide the client with the comfortable working environment to the user.